As a rotating mechanism of a rotating table device, mainly one of two systems, namely, a worm gear system and a direct drive system, is employed, and a clamping mechanism is provided in order to hold the indexing position of a rotating table during processing. In the case of a worm gear system, even in a stationary state, a minute amount of play occurs in an amount corresponding to the amount of backlash between a worm and a worm wheel. The clamping mechanism is employed in order to keep the rotating table in a stationary state without causing the play.
On the other hand, in the case of a direct drive system, a clamping mechanism is employed as a mechanism other than a motive power of a motor, which is used to hold the rotating table in a stationary state.
There are multiple types of clamping systems for realizing a clamping mechanism. Among them, a clamping mechanism based on a disk clamp system has a structure in which a brake disk, which is rotated together with a spindle that transmits a rotational force generated by the rotational drive device to the rotating table, is sandwiched between a piston, which is pneumatically or hydraulically driven, and a fixed member. By sandwiching the brake disk between the piston and the fixed member, the spindle and the rotating table connected thereto are kept in stationary states by means of frictional forces generated between the brake disk and the fixed member (for example, see Patent Literature 1).
Because the clamping mechanism is generally actuated by the action of pneumatic pressure, hydraulic pressure, or the like, it cannot be operated when a power supply to a pressure generator is halted due to a power outage or the like.
Because a rotating mechanism based on a worm gear system exhibits irreversible rotation whereby a rotational force is not transmitted from the output side to the input side, the rotating table is not rotated during a power-supply stoppage.
However, a rotating mechanism based on a direct drive system loses the holding power of a motor when the power supply to the motor is cut off, and the rotating table ends up being rotated so as to reach a stable point due to an inertial force of rotation or unbalanced torque due to a workpiece and a jig. The workpiece and a tool may become damaged when this rotation causes the workpiece and the tool to collide with each other.
In order to prevent these problems, a clamping mechanism employed in a rotating mechanism based on a direct drive system is normally provided with a biasing mechanism that biases the clamping mechanism in a clamping direction when a pneumatic pressure or a hydraulic pressure is not applied thereto (for example, see Patent Literature 2). In addition, there are systems in which another clamping device that generates a holding power only during a power-supply stoppage is provided, in addition to the clamping mechanism for holding the indexing position (for example, see Patent Literature 3).
In some cases, a disc-shaped plate spring is used as the biasing mechanism provided in the clamping mechanism that holds the indexing position of the rotating table. The plate spring has, in addition to a function for holding the clamped state by means of a restoring force generated by elastic deformation, a function for increasing the clamping torque by also utilizing, in addition to the frictional force between the fixed member and the brake disk, the frictional force between the piston and the brake disk to hold the brake disk by preventing the piston from being rotated.